1. Field of the Invention
The present method relates to a method and a program for calibrating a measuring signal of an exhaust gas probe or a control signal of a fuel dosing device of a vehicle equipped with a hybrid drive including an internal combustion engine and at least one electric motor, the vehicle also being able to be driven by an electric motor alone.
2. Description of the Related Art
Modern motor vehicles usually have one or more exhaust-gas sensors disposed in the exhaust duct, which emit a measuring signal that is proportional to the concentration of at least one exhaust-gas component and allows its concentration to be determined. Prevalent are what is referred to as broadband lambda probes, whose measuring signal supplies information about the oxygen concentration in the exhaust gas, and thus about the air-fuel ratio supplied to the internal combustion engine. Likewise known are so-called NOx sensors, which are also able to determine the oxygen concentration in the exhaust gas. To obtain reliable measuring accuracy, such probes in the vehicle must be adjusted or calibrated on a regular basis. Such a calibration usually takes place when the vehicle is in a trailing throttle mode. The trailing throttle mode is characterized by the fact that no fuel is injected, yet the vehicle continues its movement due to its inertia and drags the internal combustion engine along in the process. Depending on the position of the control elements for controlling the air supply, the dragged internal combustion engine supplies pure air having a known oxygen concentration into the exhaust gas system in this trailing throttle mode. Following a certain purging period, pure air is therefore present at the installation location of the exhaust gas sensor to be calibrated. An oxygen concentration, measured with the aid of a lambda probe, for instance, is then compared to the known oxygen concentration of the air and a correction value is calculated therefrom, which is used to correct the measured value of the lambda probe in the subsequent operation. In a similar manner, corrective functions of other sensors take place in a trailing throttle operating mode.
Furthermore, from published German patent application document DE 199 45 618 A1 a method is known for calibrating fuel dosing devices, in which the control signal of a fuel dosing device is increased in a trailing throttle operating mode until a measured oxygen concentration drops below the known oxygen concentration of air. In this way the minimum signal strength that is required to induce the fuel dosing device to inject a recognizable fuel quantity is determined, and a corrective value is calculated therefrom, which is used in the subsequent operation to correct the control signal of the fuel dosing device.
In the case of hybrid vehicles, such an adjustment is problematic. Hybrid vehicles are motor vehicles in which at least two drive units are combined with each other. For example, known hybrid vehicles use internal combustion engines and electric machines simultaneously.
In the context of the present invention, a hybrid drive of a vehicle in particular refers to a drive of a vehicle that encompasses at least one combustion engine and furthermore one electric motor, in which case the electric motor is also able to drive the vehicle by itself, i.e., without active or passive participation of the combustion engine.
Within the meaning of the present invention, hybrid drives in particular differ from conventional drives which are equipped with a combustion engine and only an electric starter or starter motor. In such drives the electric starter or starter motor is set up merely to drag the combustion engine. In other words, to the extent that a mechanical action of the electric starter or starter motor on the drive of the vehicle is conceivable, this action merely consists of dragging the internal combustion engine, in the presence of additional mechanical coupling of the internal combustion engine to the drive of the vehicle. Direct mechanical coupling of the electrical starter or starter motor to the drive of the vehicle that does not include the internal combustion engine does not take place, however. In these types of drives the vehicle is therefore unable to be driven solely by the electric starter or starter motor; instead, a mechanical action takes place indirectly at best, transmitted by the internal combustion engine.
The properties of internal combustion engines and electric machines advantageously complement one another in a hybrid vehicle. Especially preferred these days are so-called parallel hybrid concepts, in which the vehicle drive is able to be represented both by the internal combustion engine and the electric motor(s) simultaneously. In addition, there are also so-called series hybrid concepts, in which the driving of the vehicle takes place via one or more electric motor(s) exclusively, while the internal combustion engine generates the electrical current for recharging an energy store via a separate generator, the electric current then supplying the electric motor(s). The current may also be supplied directly to the electric motor(s). A trailing throttle operation is usually not desired in hybrid vehicles of this type. Instead, when no torque is required, the internal combustion engine is meant to be decoupled from the drive train, and the internal combustion engine is to be restarted when required. In this respect, it is even problematic to generate a trailing throttle operation in such hybrid vehicles. Especially problematic, however, is to provide a trailing throttle operation of sufficient length. For if the trailing throttle operation is activated only when needed, for instance by means of a trailing throttle coordinator, then the problem is encountered that the trailing throttle phase must have a certain minimum length for the lambda probe adjustment, and also for other adjustment functions. Since the duration of the trailing throttle phase is not known in advance, the coordinator often requests the trailing throttle although the ensuing trailing throttle phase does not have the desired length and consequently is unable to be utilized. This in turn worsens the energetic overall efficiency of the hybrid vehicle.